Leading edges of structures for hypersonic flight are subject to high heat loads. They either have to be made of ablative material (sacrificial), or they need to be cooled. Most previous applications were ablative, (i.e. rocket noses, mercury, apollo), or were not conducive to small leading edge pieces as required in some new applications. Space shuttle tiles are not suitable for small nosepieces because they could not stand the heat flux generated on a small radius nose. No known material can withstand these heat fluxes if uncooled.
With a reusable air breathing vehicle there is a need for a leading edge that does not have to be replaced each flight. With air breathing engines mounted externally on these vehicles the leading edge heat flow problem is compounded. The interference shock wave caused by interference between the shock wave from the nose of the aircraft and from the leading edge of the engine inlet cowl creates extremely high leading edge heating. This creates higher heat fluxes than previously experienced. Also the leading edge of this type requires a small radius nosepiece for aerodynamic reasons.
The interference shock wave causes an extreme heating in an area over a width of about 10/1000 of an inch. Beyond this area there is a sharp drop off in heat loading to a high, but less extreme level. The localized heat flux can reach 100,000 btu's/ft.sup.2 sec. The ability to locally remove this heat is critical to successful operation of any leading edge protection arrangement. Not only must the heat be removed rapidly from the interior surface of the leading edge, but the material thickness must be sufficiently minimized because of the temperature rise across the metal thickness at such high heat rates.
It is also important to effectively remove heat from the heat pipe in order to keep the operating temperature level within the heat pipe to an appropriate level.